A typical magnetoresistive element has a magnetization fixed layer whose magnetization direction is fixed, a magnetization free layer whose magnetization direction is reversible, and a nonmagnetic layer sandwiched by the magnetization fixed layer and the magnetization free layer. In a case where the nonmagnetic layer is a thin insulating layer, the magnetoresistive element is called a TMR (Tunnel MagnetoResistance) element or an MTJ (Magnetic Tunnel Junction) element. A resistance value of the magnetoresistive element varies depending on whether magnetization directions of the magnetization fixed layer and the magnetization free layer are parallel or anti-parallel to each other. A memory that nonvolatilely stores a data by utilizing such a change in the resistance value of the magnetoresistive element is a magnetic random access memory (MRAM: Magnetic Random Access Memory).
Meanwhile, a logic device using such a magnetoresistive element is proposed (refer, for example, to Japanese Patent Publication JP-2004-6775, Japanese Patent Publication JP-2005-235307, Japanese Patent Publication JP-2006-24714, Japanese Patent Publication JP-2008-99284 and Japanese Patent Publication JP-2006-526907). Japanese Patent Publication JP-2004-6775 among them describes a logic gate (magnetic logic element) that can achieve various logic functions by using a magnetoresistive element.
FIG. 1 schematically shows a configuration of a magnetic logic element 100 described in the Japanese Patent Publication JP-2004-6775. The magnetic logic element 100 has two magnetoresistive elements 110 and 120, and the two magnetoresistive elements 110 and 120 are laminated across an intermediate section SP. The first magnetoresistive element 110 has a laminated structure that a hard magnetic section HM1, a spin transfer intermediate section NM1 and a soft magnetic section SM1 are laminated. On the other hand, the second magnetoresistive element 120 has a laminated structure that a hard magnetic section HM2, a spin transfer intermediate section NM2 and a soft magnetic section SM2 are laminated. The hard magnetic sections HM1 and HM2 each corresponds to the magnetization fixed layer whose magnetization direction is fixed. On the other hand, the soft magnetic sections SM1 and SM2 each corresponds to the magnetization free layer whose magnetization direction is not fixed. The soft magnetic sections SM1 and SM2 are provided on both sides of the intermediate section SP.
The magnetization directions of the soft magnetic sections SM1 and SM2 are controlled by a spin transfer method. According to the spin transfer method, a current is supplied in a perpendicular direction between the soft magnetic section and the hard magnetic section through the spin transfer intermediate section, and the magnetization direction of the soft magnetic section is switched by spin transfer due to spin-polarized electrons. For this purpose, the hard magnetic section HM1, the soft magnetic section SM1, the soft magnetic section SM2 and the hard magnetic section HM2 are connected to electrodes E1, E2, E3 and E4, respectively. It is possible by inputting input signals to the electrodes E1 and E2 to control the magnetization direction of the soft magnetic section SM1 of the first magnetoresistive element 110. Similarly, it is possible by inputting input signals to the electrodes E3 and E4 to control the magnetization direction of the soft magnetic section SM2 of the second magnetoresistive element 120. A logical value of the magnetic logic element 100 is determined depending on a relationship (parallel or anti-parallel) between the respective magnetization directions of the soft magnetic section SM1 and the soft magnetic section SM2.
Regarding the magnetic logic element 100, two input signals (A, B) are appropriately input to the electrodes E1 to E4. As a result, the magnetic logic element 100 can achieve logic functions such as EXOR, EXNOR, AND, NAND, OR and NOR. In other words, it is possible to reconfigure the logic function. This kind of element is referred to as a “reconfigurable logic gate”.